Many communications system use encryption to protect communicated data from unauthorized interception. In an encryption system, the message to be hidden (sometimes called “plaintext”) is modified in a reversible way (by a process sometimes referred to as “encryption” which can be performed by an “encrypter”) such that the substance of the message is hidden. The resulting encrypted message (sometimes called “ciphertext”) can then be transmitted across an unsecured (e.g., subject to eavesdropping or interception) channel. Upon reception, the original message is recovered by reversing the modification (by a process sometimes referred to as “decryption” which can be performed by a “decrypter”). To ensure that only the desired recipient can properly decrypt the encrypted message, some aspect of the encryption algorithm is kept secret. Typically, the encryption algorithm operates using a secret key, while the details of the algorithm may be publicly disclosed. Keys are distributed through various means to the users authorized to transmit/receive encrypted communications, and users may have one or more different keys. Some variations on this basic process (e.g., “public key” cryptosystems) can also be used.
In some circumstances, multiple encrypted communications links may need to be processed. For example, a multiplexed stream of data may include data for multiple users. If the multiplexed stream of data was encrypted using a single encrypter after it was multiplexed together, the resulting ciphertext stream can be decrypted and then demultiplexed. In other words, the encryption and decryption process is common for all users. Such a technique, however, provides limited flexibility.
In other circumstances, multiple encrypted communications links may each use their own associated encryption. Generally, the communications streams must be separately decrypted by corresponding decrypters. A communications node which uses many communications links may therefore include a large number of decrypters. This can result in undesirable size, weight, and power consumption.